Semi-automatic gearbox system including improved control means for when the vehicle is stationary

ABSTRACT

The present invention relates to a semi-automatic gearbox system, characterized by the fact that it includes means suitable for causing first gear to be engaged automatically when the system detects that the vehicle has stopped, with the engine running, and with a gear ratio other than neutral or than reverse.

The present invention relates to gearboxes for motor vehicles.

It is known that some of the vehicles on the market today are equippedwith "manual" gearboxes, and others are equipped with "automatic"gearboxes.

In a manual gearbox, the gear ratio engaged is chosen unambiguously bythe driver, by means of a suitable lever, and the gears are selected orchanged mechanically and directly by the lever.

Conversely, in an automatic gearbox, the driver has access, via a lever,only to a choice of a forward drive mode (low gear or high gear), areverse drive mode, or a disengaged or neutral position (also referredto as "park"). On this basis, a module automatically moves the gearboxthrough both directions in which the gear ratios change, i.e. going bothup through the gear ratios and down through them, without the driverbeing able to impose a precise choice of gear.

Automatic gearboxes are quite well accepted by certain drivers. However,they are not universally liked. In particular, they are not very wellaccepted in Latin countries.

In recent years, some companies have proposed vehicles equipped with"semi-automatic" gearboxes.

Accompanying FIG. 1 is a diagram showing the overall structure of such aconventional semi-automatic gearbox system.

Such a system includes a conventional gearbox 10 provided with actuators20, which are generally fluid-driven servo-controlled actuators,suitable for acting on the gearbox 10 to change gears on the basis ofinstructions issued by a control assembly 30. The control assembly 30comprises a manually-actuated control lever 32 and control transducers34 that respond to the control lever 32 being displaced by defining gearchange instructions. The control assembly 30 is associated with anelectronic module 40 which receives the above-mentioned changeinstructions generated by the control transducers 34. The electronicmodule 40 controls the actuators 20 associated with the gearbox 10. Inaddition, the electronic module 40 is generally connected to sensors,e.g. a vehicle speed sensor 50, so that the electronic module 40controls execution by the actuators 20 of the change instructions issuedby the control assembly 30 as a function of the speed of the vehicle.For this purpose, the electronic module 40 applies instructions outputby the control assembly 30 to the actuators 20 only if said instructionsare compatible with the operating conditions of the vehicle.

The driver thus remains in control of choosing which gear ratio isengaged, because the driver acts on the lever 32 to request a change ofgear (going up through the gears or going down through them, or else achange to reverse gear). However, the electronic module 40 oversees thesystem as a whole, and it authorizes a gear change only if the operatingconditions of the vehicle are compatible with the change.

Such semi-automatic gearbox systems offer numerous advantages over otherprior systems:

they make driving more comfortable;

they make it possible to omit the clutch pedal, as with an automaticgearbox;

they make it possible to change gear without taking the foot off theaccelerator, when provision is made to integrate the gearbox system intothe engine control system;

they can be implemented at an intermediate cost between the cost of amanual gearbox and the cost of an automatic gearbox;

they fully maintain the pleasure of driving;

they make it possible to improve fuel consumption, power, and enginewear as compared with manual gearboxes;

they extend the life-spans of the various members;

they improve driving safety as compared with manual gearboxes; and

they are compatible with conventional manual gearboxes.

Document EP-A-0 584 984 describes a control device for an automatic orsemi-automatic motor vehicle gearbox in which a predetermined gear ratiofor starting is engaged automatically if the speed of the vehicle islower than a given value.

However, in spite of all those advantages, semi-automatic gearboxsystems have not been as commercially successful as expected.

An object of the present invention is to improve semi-automatic gearboxsystems.

In a first aspect, the object is achieved by the present invention bymeans of a semi-automatic gearbox system, characterized by the fact thatit includes means suitable for causing first gear to be engagedautomatically when the system detects that the vehicle has stopped, withthe engine running, and with a gear ratio other than neutral or thanreverse.

In a second aspect, the object is achieved by the present invention bymeans of a semi-automatic gearbox system, characterized by the fact thatit includes means suitable for controlling an automatic operating modefor changing gear ratios in the gearbox.

In a third aspect, the object is achieved by the present invention bymeans of a semi-automatic gearbox system, characterized by the fact thatit includes means suitable for managing and detecting a low-grip mode inwhich the vehicle wheels are gripping poorly, and for responding to sucha detection by imposing management suitable for minimizing variations inthe engine torque transmitted to the wheels.

Other characteristics, objects, and advantages of the present inventionappear on reading the following detailed description with reference tothe accompanying drawings which are given by way of non limiting exampleand in which:

FIG. 1 (described above) is a block diagram of a prior artsemi-automatic gearbox system;

FIG. 2 is a diagrammatic view of a system of the present invention;

FIG. 3 is a block diagram of a system of the present invention;

FIG. 4 is a flow chart showing how the present invention operates inautomatic mode;

FIG. 5 is an example of a chart for automatic mode operation; and

FIG. 6 is a diagram showing how the clutch is controlled.

Accompanying FIG. 2 gives an overall view of the semi-automatic gearboxsystem of the present invention, which mainly comprises:

an internal combustion engine 110;

a manual gearbox 100;

two actuators 200 and 202 placed on the casing of the gearbox 100respectively for engaging/disengaging gear ratios and for selecting gearratios;

an additional actuator 204 associated with the clutching/declutchingsystem so as to control it;

a control assembly 300 which comprises a manually-actuated control lever320 and control transducers 340 that respond to the control lever 320being displaced by defining gear change instructions; and

an electronic module 400 which receives the above-mentioned changeinstructions generated by the control transducers 340, and whichcontrols the actuators 200, 202, and 204 associated with the gearbox 100and with the clutch, via a hydraulic control unit 210.

The electronic module 400 may be connected merely to a sensor 120 forsensing the revolutions of the engine of the vehicle so that theelectronic module 400 controls execution by the actuators 200, 202, and204 of the gear change instructions issued by the control assembly 300as a function of the engine speed.

However, the electronic module 400 is preferably also connected directlyto the computer 500 for managing the engine.

The module 400 can thus take advantage of the information available onthe computer 500 (in particular the instantaneous engine torque, enginespeed, i.e. engine revolutions, and revolutions at the outlet of thegearbox), and it can also control the computer to manage the enginetorque, e.g. by acting on the air intake throttle 510 or on theinjection control. In particular while changing gear, the module 400controls the computer 500 so that it manages the engine revolutions orthe torque delivered by the engine so as to avoid jolts or judderingduring gear changes.

The co-operation between the module 400 and the computer 500 preferablycontrols each gear change in the form of a sequence of four steps asfollows:

1) in a first step, the module 400 requests the computer 500 to reducethe torque delivered by the engine, and then causes declutching to takeplace;

2) in a second step, the module 400 disengages the previouslyimplemented gear ratio;

3) in a third step, the module 400 causes the newly selected gear ratioto be selected, synchronized, and engaged (in gearboxes with nosynchromesh, the gear ratio is engaged only once the primary shaft ofthe gearbox has reached the required revolutions); and

4) in a fourth step, the module 400 requests the computer 500 tore-establish engine torque and causes the clutch to be engaged.

Accompanying FIG. 3 is a block diagram showing the system in moredetail.

In addition to the elements described above with reference to FIG. 2,FIG. 3 shows the following elements:

a display 410 associated with the module 400 for displaying the engagedgear to the driver;

an accelerator pedal 520 associated with a position sensor 522 connectedto the module 400 and to the computer 500;

a hydraulic power unit 212 associated with oil pressure/level sensors214 connected to the module 400, and electrically driven control valves216 which are controlled by the module 400 and which control theactuators 200, 202, and 204;

position sensors 206 associated with the actuators 200, 204, and 206,and connected to the module 400 to monitor the real positions of theactuators;

rotation sensors 102 placed at the inlet and at the outlet of thegearbox 100, and connected to the module 400; and

interface means 530 placed between the computer 500 and the engine 110to transform the electrical output from the computer 500 into a commandfor setting the air intake control flap (throttle).

Overall operation of the above-described system is as follows.

When actuated by the driver, the gear lever 320 transmits the driver'srequest to the computer 400 via the sensors 340. After analyzing thelegitimacy of the driver's request, the module 400 proceeds to changegear as requested.

The module 400 controls the electrically driven clutching, selection,and engagement control valves 216, and establishes dialog with theengine control computer 500 so as to manage the engine torque and theengine speed appropriately during the gear change.

The commands are confirmed by the position sensors 206 on the actuators200, 202, and 204, and by the sensors 102 and 120 for sensing the enginerevolutions, and the revolutions at the inlet and at the outlet of thegearbox 100.

The absolute gear ratio engaged in the gearbox 100 is displayed on thedisplay 410.

Three important additional characteristics of the present invention arespecified below.

According to a first of the additional characteristics of the invention,the module 400 is provided with means 420 suitable for controlling anautomatic operating mode for changing gear in the gearbox 100. Whenthese means 420 are activated, the gear changes are initiated andtriggered by the module 400 itself, and not by the driver.

For this purpose, the means 420 preferably include a memory that storesthe information required to change gear, in particular the charts of thegear changes as a function of the position of the accelerator pedal 520,of the engine speed, and of the vehicle speed.

The quality of gear changing in this automatic operating mode takes intoaccount the fact that the system acts on a conventional manual gearboxwith discrete gear ratios.

Accompanying FIG. 5 shows a non-limiting example of a chart, containedin the means 420, of gear ratio changes as a function of the position ofthe accelerator pedal 520, of the engine speed, and of the vehiclespeed. In FIG. 5, the gear change curves are drawn in thick lines,whereas the gear ratio curves are drawn in fine lines.

When the system is placed in automatic operating mode, gears are changedautomatically by using the charts shown in FIG. 5, and without thedriver intervening.

They may be automatic gearbox charts which are conventional for a personskilled in the art.

The means 420 of the module 400 preferably make it possible to storethree fixed families of charts corresponding to "economy", "comfort",and "sports" driving conditions, but they do not make it possible forthe three families to be managed self-adaptively. The driver selects oneof the three families of charts, e.g. by means of a selection button.

The numerical values given in FIG. 5 are given solely by way of example.In practice, the curves must be defined specifically for eachapplication (type of vehicle).

More precisely, going over to automatic mode may be achieved either a)manually, by means of a control 322 available to the driver, or b)automatically.

The control 322 available to the driver is preferably formed by amonostable button placed, for example, on the lever 320. By activatingthis control 322, the driver can decide to go over to automatic mode.

Preferably, activating the control 322 defines a transient automaticstate, i.e. the module 400 acquires automatic control of gear changingonly after the control 322 has been activated. In addition, the module400 maintains the automatic operating mode so long as the driver doesnot act on the gear shift control lever 320, and it cancels theautomatic operating mode whenever the lever 320 is acted on.

Accompanying FIG. 4 is a flow chart corresponding to such an automaticoperating mode as requested by the driver.

By examining this flow chart, it can be understood that going over fromthe automatic mode to the "manual" mode, i.e. to the mode in which gearchanging is controlled by the lever 320, takes place only at thedriver's initiative. As soon as the driver acts on the lever 320, themodule 400 goes over to manual mode, causing engagement of the next gearup or the next gear down from the gear in which the gearbox 100 wasengaged in automatic mode. The "neutral" or "reverse" commands also actimmediately (to go over from automatic mode to normal mode), if the gearchange conditions are satisfied. However, there is an exception to theabove rule: when the vehicle is stationary, or while parking maneuversare being performed from such a stationary position, the system remainsin automatic mode in spite of any intervention by the driver on thelever to select a forward gear or a reverse gear.

In a variant, it is also possible to go over from automatic mode tomanual mode by acting on the control 322 (e.g. a monostable button).

The advantage of using a monostable button for selecting automatic modeis that the driver does not have to perform a plurality of operations toreturn to manual mode.

When the driver quits automatic mode, the module 400 abandons any gearchange that is being made at the time at which the lever 320 isactuated.

Preferably, on switching off, the system retains the previously existingoperating mode.

Going over automatically to the automatic operating mode is decided by asubassembly of the means 420 when the module 400 no longer recognizesthe requests made by the driver, as expressed by the lever 320 beingactuated.

In which case, the automatic mode is preferably a degraded operatingmode in which the module 400 limits the gear ratio changeauthorizations, e.g. by authorizing only changes up to third gear for a5-speed gearbox. Such a degraded mode in particular prompts the driverto go to a maintenance workshop to identify and repair the causes of thefailure to recognize instructions output by the transducers 340.

According to a second additional characteristic of the invention, themodule 400 is provided with means 430 suitable for causing first gear tobe engaged automatically when the system detects that the vehicle hascome to a halt, with the engine 110 running, and with a gear ratio otherthan neutral or than reverse.

These means 430 make it possible in particular when the vehicle hasstopped, e.g. at traffic lights, for the vehicle to start offimmediately, the acceleration being determined by the accelerator pedal520.

Preferably, the system further includes a device 440, e.g. an audibledevice, suitable for warning the driver of dangerous situations, e.g. ofthe type in which the vehicle is stationary, with the engine running,with first gear engaged, and with a door open.

The system assumes that the vehicle is stationary when the engine speed(as detected by the sensor 120) and the inlet speed and the outlet speedof the gearbox 100 (as detected by the sensors 102) are below minimumthresholds for a predefined lapse of time T.

This parameter T can be configured differently depending on whether ornot the vehicle is equipped with an Anti-Blocking System (ABS).

When the vehicle is not equipped with an ABS, the time T is longer so asnot to confuse a period during which the vehicle is stationary with aperiod during which the vehicle is skidding with its wheels blocked,e.g. on ice.

In a typical embodiment, the means 430 are suitable for causing firstgear to be engaged automatically when:

the lever 320 is in the rest position; and

the system is not in the automatic operating mode; and

the gear ratio engaged is a gear that corresponds to a gear higher thanfirst gear; and

the engine speed is higher than a threshold, e.g. 400 revolutions perminute (r.p.m.); and

the speed of the primary shaft of the gearbox 100 is lower than athreshold, e.g. 200 r.p.m.; and

the speed of the differential outlet shaft is lower than a threshold,e.g. 50 r.p.m.

The means 430 cause first gear to be engaged by causing the following tooccur successively:

the old gear (2nd to 5th gear) is disengaged;

the position containing first gear is selected; and

first gear is engaged.

During all of these operations, the clutch remains disengaged.

According to a third additional characteristic of the invention, themodule 400 is provided with means 450 suitable for detecting a low-gripmode in which the vehicle wheels are gripping poorly, and for respondingto such detection by constraining the module 400 to manage gear changingin such manner as to minimize variations in the engine torquetransmitted to the wheels.

Preferably, the means 450 perform this management by differentparameterization for the relationships governing the following:

reducing the engine torque as requested to the computer 500 prior to thegear change;

declutching prior to the gear change;

clutching after the gear change;

re-establishing the engine torque as requested to the computer 500 afterthe gear change; and

clutching while the vehicle is starting.

Furthermore, the means 450 are preferably suitable for automaticallyconstraining the gearbox to change into second gear when the vehiclestops and when low-grip conditions are detected.

It should be noted that the time required for changing gear is increasedwith the above process. However, the time during which traction is lostduring the gear change remains unchanged because this time spans onlythose actions (disengagement, selection, engagement) which do notinfluence the variations in transmitted engine torque.

The times required for reducing and re-establishing the torque and fordeclutching and clutching are longer than in the normal-grip mode anddifferent (longer) when changing down than when changing up.

Going over to low-grip mode may take place a) manually, by the driveractuating a suitable control 323, or b) automatically.

The control 323 is preferably formed by a bistable button having twopositions, namely a first position corresponding to a low-grip operatingmode and a second position corresponding to a normal-grip operatingmode.

When the means 450 detect that the control 323 has switched over to afirst position, i.e. they detect the low-grip mode in which the wheelsdo not grip very well, they directly initiate the management suitablefor minimizing the variations in the engine torque transmitted to thewheels.

The means 450 are provided with a sub-assembly suitable for detecting a"blocked wheels" situation, e.g. by examining a corresponding output onan ABS computer, and for responding to such detection by automaticallyswitching over to low-grip mode.

Returning to normal-grip mode from low-grip mode may take place eithera) manually by means of the control 323 (for this purpose, the driveracts on the button 323 to put it back in its second position), or b)automatically (in which case, the module 400 automatically puts thesystem back into normal mode once it no longer receives a "wheelsblocked" signal).

Preferably, the clutch associated with the engine 110 is controlled in aclosed loop by the module 400 using an algorithm of the proportionalintegral (PI) type, as shown in the control diagram given in FIG. 6.

With reference to FIG. 6:

Δω•_(ref) is a reference to be reached equal to the differentiateddifference between a reference engine speed ωeng and the reference speedω1 of the primary shaft of the gearbox; the value Δω•_(ref) correspondsto a parameter imposed on the system by the module 400 as a function ofthe position of the accelerator pedal and of the change in gear takingplace;

X•_(ref) is the differentiated position of the clutch actuator 204; itis a parameter imposed on the system (objective to be reached) as afunction of the position of the accelerator pedal and of the change ingear taking place;

PI is the PI-type control algorithm;

i is the current for controlling the electrically driven clutch valve;

EV is the electrically driven clutch valve;

X_(measured) is the position of the clutch actuator 204 as measured bythe position sensor associated therewith;

ωENG_(measured) is the engine speed as measured;

ω1_(measured) is the primary shaft speed as measured; and

Δω•_(measured) is the differentiated difference between the engine speedas measured and the primary shaft speed as measured.

As shown in FIG. 6, the clutch servo-control loop comprises:

an adder 401 which sums the above-mentioned parameters ανδΔω•_(measured);

a calculator module 402 that integrates the signal output from the adder401 to a limit X•_(ref) max, and that outputs the signal X•_(ref) ;

an adder 403 which sums the signal X•_(ref) and the signal X•_(measured)(which is equal to the derivative of the signal X_(measured) generatedby the sensor associated with the clutch actuator 204);

a calculator module 404 which applies the PI-type control algorithm tothe signal output by the adder 403, and which generates at its outputthe current i for controlling the electrically driven clutch valve;

the electrically driven valve EV controlled by the current i;

the clutch actuator 204 equipped with the position sensor delivering thesignal X_(measured) ;

a calculator module 405 which calculates the derivative X•_(measured) ofthe signal generated by the sensor; and

a calculator module 406 which calculates the differentiated differenceΔω•_(measured) between the engine speed as measured ωENG_(measured) andthe primary shaft speed as measured ω1.

The low-grip mode is obtained by giving appropriate values to theparameters Δω•_(ref) and X•_(ref) so that the clutch closes more slowlyand so that the variations in the engine torque transmitted to thewheels are minimized.

Naturally, the present invention is not limited to the particularembodiments described above, but rather it extends to any variantcomplying with the spirit of it.

I claim:
 1. A control system for a semi-automatic gearbox installed in avehicle, including means suitable for detecting when the vehicle isstationary by detecting when an engine speed, an inlet speed and anoutlet speed of the gearbox are below minimum thresholds for apredefined time T, and causing first gear to be engaged automaticallywhen said system detects that the vehicle is stationary, with the enginerunning, and with a gear ratio other than neutral or than reverse.
 2. Asystem according to claim 1, characterized by the fact that it includesa signaling device suitable for warning a driver of dangeroussituations.
 3. A system according to claim 1, characterized by the factthat it includes a signaling device suitable for warning a driver ofdangerous situations of the type in which the vehicle is stationary,with the engine running, with first gear engaged, and with a door of thevehicle open.
 4. A system according to claim 2, characterized by thefact that the signaling device (440) is an audible device.
 5. A systemaccording to claim 1, characterized by the fact that the predefined timeT can be configured differently depending on whether or not an ABS ispresent.
 6. A system according to claim 1, characterized by the factthat it includes a control device suitable for causing first gear to beengaged automatically when;a control lever is in a rest position; andthe system is not in the automatic operating mode; and the gear ratioengaged is a gear that corresponds to a gear higher than first gear; andthe engine speed is higher than a threshold; and the speed of a primaryshaft of the gearbox is lower than a threshold; and the speed of adifferential outlet shaft is lower than a threshold.
 7. A systemaccording to claim 1, characterized by the fact that it includes controlmeans suitable for controlling an automatic operating mode for changinggear ratios in the gearbox.
 8. A system according to claim 7,characterized by the fact that the control means (420) include a memorywhich stores information required to change gear ratios.
 9. A systemaccording to claim 7, characterized by the fact that the control meansinclude a memory which stores charts for changing gear as a function inparticular of position of an accelerator pedal of the engine speed, andof the vehicle speed.
 10. A system according to claim 9, characterizedby the fact that the control means (420) store a plurality of gearchange charts that can be selected by the driver.
 11. A system accordingto claim 9, characterized by the fact that the control means (420) storethree charts corresponding respectively to "economy" driving, to"comfort" driving, and to "sports" driving, the charts being selectableby the driver.
 12. A system according to claim 9, characterized by thefact that the control means include a control available to the driverfor initiating an automatic operating mode, and where applicable forinitiating a change over from automatic mode to manual mode.
 13. Asystem according to claim 12, characterized by the fact that the controlavailable to the driver is formed by a monostable button.
 14. A systemaccording to claim 12, characterized by the fact that the control isplaced on a lever for controlling gear changes.
 15. A system accordingto claim 12, characterized by the fact that the control available to thedriver defines a transient automatic state.
 16. A system according toclaim 12, characterized by the fact the control available to the driverdefines a transient automatic state in which a control module maintainsthe automatic operating mode so long as the driver does not act on agear shift control lever or on the control itself, thereby canceling theautomatic operating mode.
 17. A system according to claim 1,characterized by the fact that it includes a subassembly suitable forimposing an automatic operating mode when it no longer recognizesrequests made by the driver, as expressed by actuating a lever.
 18. Acontrol system, for a semi-automatic gearbox installed in a vehicle,including means for detecting when the vehicle is stationary bydetecting when;a control lever is in a rest position; and said system isnot in an automatic operating mode; and the gear ratio engaged is a gearthat corresponds to a gear higher than first gear; andwhen for apredefined time T: the engine speed is lower than a threshold; and thespeed of the primary shaft of the gearbox is lower than a threshold; andthe speed of the differential outlet shaft is lower than a threshold,and causing first gear to be engaged automatically when the systemdetects that the vehicle is stationary, with the engine running, andwith a gear ration other than neutral or than reverse.